This invention relates to channeled glass articles such as neon lighting devices. This invention also relates to a stretched seal forming process for making the glass articles.
Neon lighting devices are disclosed in U.S. Pat. No. 4,584,501 (Cocks et al.), U.S. Pat. No. 4,990,826 (Cocks et al.), U.S. Pat. No. 5,036,243 (Cocks et al.). Generally, these patents disclose multifaceted lighting devices comprising glass or other vitreous plates which are hermetically sealed together to form a device with internally enclosed channels. These channels are thereafter evacuated and backfilled with an inert gas such as neon and thereafter ionized through the provision of a series of electrodes.
Generally, the method for forming the glass component of these prior art neon lighting devices involves cutting channels in a bottom glass plate followed by hermetically sealing, via the use of a glass frit, a glass top plate to this channeled glass bottom plate. Various methods are used to cut the channels into the bottom glass plate including grinding, etching and sand blasting through an adhesive rubberized mask exhibiting a pattern identical in shape to the desired channel pattern.
Recently, the improved method for forming glass bodies for use as discharge fighting devices has been disclosed in U.S. patent application Ser. No. 08/634,485 (Allen et al.); co-assigned to the instant assignee, and herein incorporated by reference. Briefly, this method, involves two, separately delivered and deposited, molten glass ribbons, i.e., a sealing ribbon laid over the top of the already deposited channel-forming ribbon. For very thin products/thin ribbons, the difficulty with this method is that in order to maintain a time-efficient process, the rollers must be spaced very close together and run a very high speed; e.g. rollers spaced 12 in. apart and moved at a speed of about 17xe2x80x3/sec.
Still another improved method for forming glass bodies for use as discharge lighting devices has been disclosed in U.S. patent application Ser. No. 08/851,320 (Allen et al.); co-assigned to the instant assignee, and herein incorporated by reference. Briefly, upon exiting the rollers, first length of the molten glass ribbon is deposited upon the mold which is moved along a predetermined path, preferably a direction along the mold""s width; although the molten ribbon could be deposited in a direction along the mold""s length.
Following the conformance of the first length to the mold cavity, through either gravity or vacuum forming or a combination of the two, the mold is thereafter moved back along a second predetermined path opposite the first direction. In other words, second length of the molten glass ribbon is essentially folded over and onto first length of the molten glass ribbon.
As improved as these glass articles and methods are, the demands of the market place require improved glass articles and method for producing them. Certain lighting businesses require as little optical interference as possible. Phosphor costing do not like areas that will settle out the phosphor and create dark spots on the lamp. These glass articles are useful in vacuum tubes, incandescent lamps, fluorescent lamps, CRT""s, vehicle lighting and the like.
I have developed a method of shaping thin glass articles. As a result, the glass article has thin walls, as well as a thin glass interface between the two laminated sheets. When a layer of molten glass is applied to a mold and a second layer of glass is applied, channels are created between the glass layers. My process changes the shape of the article and modifies the internal interface at the juncture where the glass sheets separate to make channels. I use the mechanical motion of the plunger combined with plunger vacuum and internal gas pressure to make these changes. By reducing the plunger dwell time, a glass seal can be made and retain sufficient heat for the glass to be flexible. This results in a glass article, wherein the second layer of glass is thin and the juncture between layers is thin. I then utilize the glass flexibility by retracting the plunger slowly and pulling the two glass layers away from each other at the junction. This motion stretches the glass interface and straightens the glass interface surface.
Dwell time as used herein is a combination of an initial contact time and a subsequent forming time. As soon as the plunger touches the glass layers, it immediately pulls back from the junction and holds its position away from the junction. The initial contact time is less than one second and as close to zero as possible. The pull back or forming time may be as long as 2 to 3 seconds.
The stretched seal produces a stronger mechanical seal and consequently a stronger product. Another benefit of this process occurs when applying a phosphor coating. The thin interface of this invention essentially has no shape or slope. The normal xe2x80x9cuxe2x80x9d or xe2x80x9cvxe2x80x9d shaped interface of the prior art glass leaves a thick area of phosphor in the recess. See prior art FIG. 3. When the lamp is lit, the thick area of phosphor will be darker than the remaining lamp areas. When the seal is stretched with this process, the problem is eliminated. Another use of the technique is to reduce the contact area between glass layers. A reduced contact area can reduce the optical interference caused by the joining of two layers of glass. If the contact area between the sheets of glass can be reduced or minimized, the optics can be improved for products requiring uniform light distribution.
This invention eliminates the xe2x80x9cuxe2x80x9d or xe2x80x9cvxe2x80x9d shaped interface of the prior art.
In one embodiment, the glass articles of this invention have a gentle shoulder at the interface. In another embodiment, the glass articles of this invention have virtually no shoulder at the interface. In this embodiment, the interface is nothing more than slight slope. See FIG. 2A.
The most significant value of this invention is for the fluorescent light business. The phosphor coatings do not like areas that will settle out the phosphor and create dark spots in the lamps. The glass thickness can also be reduced to make thinner products of complex geometry. The back lighting businesses require as little optical interference as possible in the lens area. With this process, we can build thin unobtrusive support structures within a lamp and minimize the optical interference.